1. Field of the Invention
This invention relates to an apparatus and a method for epitaxial growth of a III-V nitride film including at least Al element on a substrate by using a Hydride Vapor Phase Epitaxy(HVPE) method.
2. Related Art Statement
In opto-electronic device such as light-emitting diodes and laser diodes, it is proposed that a III-V nitride film having a composition of AlxGayInzN(X+Y+Z=1) including at least Al element is epitaxially grown on a given substrate. For example, it is described in “J. Appl. Phys., 68, No. 7 (1999)”, from pp 774 onward that a GaN film is epitaxially grown on a sapphire substrate.
In this method, a Ga metallic material is charged into a reactor in which a sapphire substrate having a GaN film on its surface is held, and a hydrochloric gas is also introduced into the reactor to generate a gallium chloride gas. Then, the gallium chloride gas and an ammonia gas are reacted with each other to deposit the GaN film on the sapphire substrate. This forming process is generally called as a “Hydride Vapor Phase Epitaxy (HVPE) method”.
The HVPE method is characterized by having a larger growth rate than that of a conventional Metalorganic vapor Phase Epitaxy (MOVPE) method. For example, if the GaN film is epitaxially grown by the MOVPE method, the typical growth rate is several μm/hour. On the other hand, if the GaN film is epitaxially grown by the HVPE method, the typical growth rate is several ten-hundred μm/hour. Therefore, the HVPE method has a special advantage in fabricating a III-V nitride film having a larger thickness.
In the case of fabricating an AlN film using the above HVPE method, an aluminum metallic material and a chloride based gas are charged into a reactor to generate an aluminum chloride gas in the reactor. Then, the aluminum chloride gas and an ammonia gas are reacted with each other in the reactor to deposit the AlN film on a given substrate.
It is confirmed, however, that the AlN film with good and stable properties cannot be fabricated using the above conventional HVPE method. Therefore, the inventors of the present invention have intensely studied the causes of the deterioration in the AlN film fabricated by the conventional HVPE method, and discovered the following.
A reactor employed in the conventional HVPE method is made of silicon oxide-based material such as quartz. However, the silicon oxide-based material is likely to be corroded by an aluminum chloride gas generated through the reaction of an aluminum metallic material and a chloride-based gas to form pinholes in the reactor. As a result, air is introduced into the reactor from the outer environment of the reactor, and oxygen elements are taken into the AlN film fabricated or being fabricated to deteriorate the crystallinity of the AlN film. Such a poor crystallinity AlN film can not be used for an opto-electronic device substrate.
Moreover, if the pinholes are formed in the reactor through the corrosion of the AlCl gas, various gases are leaked from the reactor to the outside to bring pollution to the outer environment, in addition to the problem that the surrounding air is introduced into the reactor.
In order to iron out the corrosion of the reactor by the AlCl gas, it is suggested that the reactor is made of a BN material or a SiNx material having large anti-corrosion property against the AlCl gas. However, such an anti-corrosion material shows only poor processing performance, and thus, can not be employed practically. Moreover, the anti-corrosion material is expensive, resulting in the higher cost of the AlN film.
The above problems due to the conventional HVPE method exist in fabricating a AlxGayInzN (X+Y+Z=1), in addition to the above AlN film.